This invention relates to a coaxial engine starter in which an armature rotary shaft of a d.c. motor, a rod of a solenoid switch and a starter output rotary shaft are disposed on a common axis.
FIG. 1 illustrates in a sectional front view one example of a conventional coaxial engine starter disclosed in Japanese Utility Model Laid-Open No. 63-71474. In FIG. 1, reference numeral 1 indicates armature of a d.c. motor, and 2 indicates the a hollow armature rotary shaft secured to the armature 1 and having a face-type commutator 3 at the rear end of the armature 1. 4 indicates a bracket made of resin and holds brushes 5 in sliding contact with the commutator 3 and has integrally molded a stationary contact 6 connected to the brush 5 and a stationary contact 8 connected to an external terminal 7. Within an inner passage 2a of the armature rotary shaft 2, an output rotary shaft 9 is disposed and axially slidably supported by a sleeve bearing 10. Mounted at the front end of the output rotary shaft 9 is a pinion 11 to which the rotation of the armature rotary shaft 2 is transmitted through a planetary speed reduction gear 12 and a drive force transmitting mechanism 13 comprising an unillustrated over-running clutch.
Reference numeral 14 indicates a solenoid switch disposed at the rear side of the d.c. motor, and 15 indicates a rod disposed on a common axis with respect to the armature rotary shaft 2 and the output rotary shaft 9. A plunger 16 is secured at the rear end of the rod 15, and a movable contact 17 is mounted through an insulating member 18 so as to be brought into contact with the stationary contacts 6 and 8 when the rod 15 is moved forward. The front end of the rod 15 is inserted into a tubular rod 19, and an intermediate rod 20 is disposed in front of the tubular rod 19 so as to transmit the forward movement of the rod 15 to the output rotary shaft 9. 21 indicated an excitation coil for moving the plunger 16 and is wound around a bobbin 22 made of a resin, and a sleeve 23 is disposed in the inner circumference side of the bobbin 22 within which the plunger 16 slides.
The operation of the above-structured coaxial engine starter will now be described, when an unillustrated starter switch of a vehicle is turned on, the solenoid switch 14 is energized to move the plunger 16 forward, this forward drive force is transmitted to the output rotary shaft 9 through the tubular rod 19 and the intermediate rod 20. Also, at this time, the movable contact 17 abuts against the stationary contacts 6 and 8 to connect the d.c. motor to the power source, so that the rotational drive force of the armature rotary shaft 2 is transmitted to the output rotary shaft 9 through the drive force transmission mechanism 13, and this rotation is transmitted to the pinion 11 which is in engagement with the engine ring gear due to the forwardly moved output rotary shaft 9 whereby the engine is started. Further, when the power source is disconnected from the solenoid switch 14 after the engine has been started, the output rotary shaft 9 is returned to its home position by a return spring, thereby to release the engagement of the pinion 11 and the engine ring gear.
As has been described, the conventional coaxial engine starter has the movable contact 17 and the stationary contacts 6 and 8 disposed with in the inner space defined by the sleeve 23. Therefore, the contact powder generated by contacting and separating of the movable contact 17 and the stationary contacts 6 and 8 as well as the wear particles generated by the vibration of the insulating member 18 supporting the movable contact 17 attach to the sliding surface (the inner circumferential surface of the sleeve 23) of the plunger 16, and the wear powders from the sleeve bearing 10 attach to the sliding surface of the plunger 16 from the inner passage 2a of the armature rotary shaft 2 through the central opening of the bracket 4, whereby these foreign matters can easily accumulate on the sliding surface to impede a smooth operation of the plunger 16.